Oriented polymer implantable device and process for making same

ABSTRACT

A device is formed by the process into a bone screw or fastener, wherein the head has a degree of polymer alignment and strength, and wherein the shank has a higher degree of polymer alignment and strength. In practice of the present invention, the polymer slug is pressed into the die cavity by the actuation of ram press, causing the slug to conform to the die cavity. Through this process, the polymer molecular orientation is aligned to different degrees, in different zones of the device.

BACKGROUND OF THE INVENTION

This application relates generally to medical implant devices and theirproduction, specifically relating to the process of manufacturing apolymer tissue and/or bone fixation device, preferably made of aresorbable polymer. The invention more particularly concerns a method ofmanufacturing a resorbable bone fixation device (e.g., screw, rod, pin,etc.) by forcing a provided polymer slug or billet into a mold while thepolymer is in a glass transition state, wherein the manufacturingprocess creates a near final shape of varying diameter and zones withvariable degrees of alignment of the polymeric molecular structure andtailored mechanical properties (e.g., higher strength).

Common techniques utilized in the past for the production of shapedpolymer materials have included, machining (e.g. milling, turning,etc.), injection molding, and extrusion. Machining a desired shape froma generic slug or billet often results in excessive waste, as the amountof material that is trimmed or cut off in making the final product willbe much greater than the amount removed during final machining of amolded or formed polymer material that is shaped nearly to final form.For example, in machining a screw shape, having a head and a threadedbody portion, from a slug or billet in the shape of a cylinder, materialmust be removed to arrive at the diameter of the head. Subsequently,more material must be removed to arrive at the desired diameter for thethreaded body portion. This extensive machining creates a great amountof chips or cut dust as waste of the material that is machined off.

Excessive waste of raw material is especially problematic in devicesconstructed of relatively expensive polymers, such as bioabsorbablepolymers and medical grade polymers, as costs are elevated due to theloss of the material, or additional costs are incurred in recapturingand recycling the material. A need exists for a manufacturing techniquethat results in higher productivity and higher yield than machining.

Injection molding is a process in which a polymer is heated to a highlyplastic state and forced to flow under high pressure filling a moldcavity, where it solidifies. Melt molding processes result in a materialhaving a relaxed orientation or molecular arrangement of the polymer asit cools, and typically does not impart great strength values, such asthose required for tissue and/or bone fixation treatments suitable forimplantation through surgical techniques (e.g., orthopedic andtraumatology applications).

It has long been known that the production of a polymer material havingan aligned orientation (i.e., not relaxed) of the polymer molecules orstructure typically results in a stronger material. This correlation hasbeen discussed in the prior art, for example see U.S. Pat. Nos.3,161,709; 3,422,181; 4,282,277; 4,968, 317; and 5,169,587, where it isdescribed that polymer materials may be drawn or extruded to cause theorientation of a semi-crystalline or crystalline polymer structure tobecome substantially aligned, thereby increasing the mechanical strengthof the material.

As discussed in U.S. Pat. No. 4,968,317 issued to Tormala et al., theprior art of using melt molding techniques such as injection molding andextrusion to make resorbable polymer implants results in strength valuesthat are typical of thermoplastic polymers. It is known that thestrength and modulus values may be increased by creating a reinforcedcomposite (i.e., incorporating reinforcing fibers), however to achievesatisfactorily large strength values with reinforced composites asimplants, the implant must necessarily be large in order to accommodatethe stresses placed upon it.

As is known, and is further described by Tormala et al., a technique forthe processing of polymer material may utilize mechanical deformation,such as drawing or hydrostatic extrusion, to alter the orientation ofthe molecular structure of crystalline structure and amorphous structureto a fibrillar state, in order to yield higher strength and elasticmodulus values. Tormala et al. describe drawing the material through theextrusion process, resulting in an extruded material that is at leastpartially fibrillated as the polymer molecules and molecular segmentsare aligned along the drawing direction. Tormala et al. in U.S. Pat. No.6,383,187 describe a resorbable screw made of the material described inthe U.S. Pat. No. 4,968,317 patent. A need exists for a fibrillarmaterial that may be created in varying cross-sections and diameters, inorder to minimize the amount of machining required to finish theproduct. A further need exists for an implantable device having variablestates or degrees of alignment of the polymer molecules. This may beaccomplished by manufacturing or processing a material that is formed tofinal part geometry or near final part geometry of a device or implant,thereby reducing the need for final machining, and also obtainingincreased mechanical strengths for implant applications.

In U.S. patent application Ser. No. 2003/0146541, Nakamura et al.describe a press molding process for the manufacture of a resorbablepolymer bonejoining device having molecular orientation. The describedprocess requires imparting the existing molecular orientation,preferably by stretching the primary article along the long axis, thenproviding the oriented primary article for press molding of the screwhead and shank threads. The press molding as applied to the polymermaterial allows the molecular orientation of the primary article to besubstantially maintained. Nakamura et al. do not describe a process forcreating a device having variable cross section and variable states ofalignment of the polymer molecules, wherein the process of manufacturingthe areas with varying cross-sections imparts an increased orientationof the polymer molecules.

In U.S. patent application Ser. No. 2003/0006533, Shikinami et al.disclose a twice-forged resorbable polymer material, wherein the polymermolecular orientation is altered by each of the forging processes tocreate “orientation along a large number of reference axes havingdifferent axial directions”. The forging steps applied to the polymerresult in the orientation of the polymer molecules to create a roomtemperature flexible material, capable of withstanding repeated bendingwithout breaking. U.S. patent application Ser. No. 2003/0006533 does notdescribe a polymer material that is shaped into varied cross-sectionsand possessing varied zones of polymer orientation.

In U.S. Pat. No. 6,232,384, Hyon discloses a resorbable bone fixationmaterial comprising a resorbable polymer, hydroxyapatite and an alkalineinorganic compound, wherein the bone fixation material is made by theprocess of providing a melt with the aformentioned components,molecularly orienting the melt through a molding or extension processand extending and orienting the chain molecules of the polymer.Preferably the molding process is performed through ram or hydrostaticextrusion. Hyon does not describe an implantable material having variedcross-section and varied zones of polymer orientation.

In U.S. Pat. No. 6,503,278, Pohjonen et al. disclose an implantablesurgical device made from a resorbable, non-crystalline (i.e.,amorphous) polymer. The amorphous material described by Pohjonen et al.is molecularly oriented and reinforced by mechanical deformation.Pohjonen et al. do not describe a polymer implant material having zonesof variable states of alignment of the polymer molecules and varyingcross section of the material.

In U.S. Pat. No. 5,431,652, Shimamoto et al. disclose a high strengthpolymer material that is hydrostatically extruded through a die underpressure to reduce voids and to form a resorbable polymer material thatretains at least 85% of its strength after 90 days implantation. Thematerial described in the Shimamoto et al. patent does not result in apolymer implant material or implant with complex geometry or variableshape other than the cross section of the die exit, nor does Shimamotoet al. arrive at or describe variable states of alignment of the polymermolecules.

In U.S. Pat. No. 6,511,511, Slivka et al. disclose a polymer implantthat is either porous or non-porous, where the material has beenreinforced by the addition of oriented fibers. The Slivka devices aremade by precipitating the polymer out from a solvent solvating thepolymer. The precipitation of the polymer causes a gel formation, whichmay then be handled and placed in a mold. Slivka et al. do not describea polymer implant having variable shape and variable states of alignmentof the polymer molecules.

The prior art described does not disclose a polymer implantable devicehaving an orientation of the polymer molecules, wherein the shapingprocess creates zones of varying cross section and orientation.

It is the intent of this invention to overcome these and othershortcomings of the prior art.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a shaped polymer articlehaving sufficient strength to serve as an implantable tissue or bonefixation device.

It is another object of the invention to provide a method ofmanufacturing the implantable device by a process that results invarying zones of polymer orientation. The degree of polymer orientationhas a correlation with the physical properties (e.g., strength,elasticity, etc.) of the material. Higher strength may be achieved byproviding higher degree of polymer orientation.

In one embodiment, a polymer slug is driven into a die cavity tooling toform an implantable device, having varied cross section and varieddegree of polymer orientation.

In a preferred embodiment of the process, the device is formed into abone screw or fastener, wherein the head has a degree of polymeralignment and strength, and wherein the shank has a higher degree ofpolymer alignment and strength.

The process of practicing the present invention (as will be furtherexplained), in its basic form, involves the steps of:

-   -   a) providing a polymer slug, die cavity tooling, and ram press,        wherein said die cavity tooling defines a die shape;    -   b) placing said polymer slug between said ram press and die        cavity tooling;    -   c) actuating said ram press in order to apply pressure upon said        slug, thereby forcing said slug to conform to said die shape,        wherein said slug is formed into a device comprising zones of        variable alignment of the polymer structure, and zones of        varying cross-section;    -   d) removing said device from said die cavity tooling; and        optionally,    -   e) shaping the device to the finished product, the shaping may        be performed by a machining procedure, a compression molding        procedure or other techniques known in the art.

DESCRIPTION OF THE DRAWINGS

FIG. 1: Depiction of cylindrical polymer slug, billet, or blank suitablefor use in the present invention.

FIG. 2A and 2B: Depictions of alternate shapes of polymer slugs,billets, or blanks.

FIG. 3A and 3B: Depictions of polymer slugs, billets, or blanks havingcomplex internal (3A) or external (3B) geometry.

FIG. 4A and 4B: Cross sectional depictions of die tooling arrangementssuitable for use in the present invention.

FIG. 5A and 5B: Depictions of press ram component having complexexternal (5A) or internal (5B) geometry.

FIG. 6: Cross sectional depiction of die tooling arrangement having ahollow core forming ejector pin.

FIG. 7: Cross sectional depiction of die tooling arrangement having asolid tip forming ejector pin

FIG. 8: Cross sectional depiction of a multi component die cavitytooling.

FIG. 9: Cross sectional depiction of die tooling arrangement havingmultiple reductions in cross section—one in the barrel component and onein the die cavity component.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention consists of a method for producing a surgicalpolymer implant, such as a tissue fixation device, or a bone fixation ortreating device. The implant may be formed in any shape suitable forimplantation into the living being and may be fastened into or ontotissue or bone (e.g. a screw, pin, rod, nail, plate, staple, sutureanchor or in the form of a similar type fastener or related component.)In the preferred embodiment, the bone treating device or implantprocessed through the method described in the present invention consistsof a bioabsorbable polymeric material or matrix. In an alternativeembodiment, the polymeric material of the implant may be non-resorbable.The polymer may feature a semi-crystalline, crystalline or amorphousstructure. A semi-crystalline or crystalline structure polymer materialfeatures an arrangement of the polymer molecules in three-dimensionalspherulitic structures and may further feature lamellae, a foldedcrystalline structure. The amorphous polymer structure generally lacksthe lamellae found in the crystalline and semi-crystalline polymerstructures. The polymer matrix material may be composed of a polymer;alternatively the material may comprise a copolymer or a mixturethereof.

The preferred, and most widely used bioabsorbable polymers to beprocessed through the application of this invention consist ofpoly(lactic acid) or PLA, poly(glycolic acid) or PGA, their copolymersand stereocopolymers such as poly(glycolide-co-L-lactide) or PGA/PLLA,or Poly-DL-lactide (DLPLA), but are not limited to these preferred orwidely used materials. Other resorbable and non-resorbable polymermaterials may be suitable for practicing this invention. Examples ofresorbable polymers that can be used to form the device are shown infollowing Table 1. These materials are only representative of thematerials and combinations of materials, which can be used in thepractice of the current invention. TABLE 1 Examples of BioresorbablePolymers for Construction of the Device of the Current InventionAliphatic polyesters Bioglass Cellulose Chitin Collagen Copolymers ofglycolide Copolymers of lactide Elastin Fibrin Glycolide/l-lactidecopolymers (PGA/PLLA) Glycolide/trimethylene carbonate copolymers(PGA/TMC) Hydrogel Lactide/tetramethylglycolide copolymersLactide/trimethylene carbonate copolymers Lactide/ε-caprolactonecopolymers Lactide/σ-valerolactone copolymers L-lactide/dl-lactidecopolymers Methyl methacrylate-N-vinyl pyrrolidone copolymers Modifiedproteins Nylon-2 PHBA/γ-hydroxyvalerate copolymers (PHBA/HVA)PLA/polyethylene oxide copolymers PLA-polyethylene oxide (PELA) Poly(amino acids) Poly (trimethylene carbonates) Poly hydroxyalkanoatepolymers (PHA) Poly(alklyene oxalates) Poly(butylene diglycolate)Poly(hydroxy butyrate) (PHB) Poly(n-vinyl pyrrolidone) Poly(orthoesters) Polyalkyl-2-cyanoacrylates Polyanhydrides PolycyanoacrylatesPolydepsipeptides Polydihydropyrans Poly-dl-lactide (PDLLA)Polyesteramides Polyesters of oxalic acid Polyglycolide (PGA)Polyiminocarbonates Polylactides (PLA) Poly-l-lactide (PLLA)Polyorthoesters Poly-p-dioxanone (PDO) Polypeptides PolyphosphazenesPolysaccharides Polyurethanes (PU) Polyvinyl alcohol (PVA)Poly-β-hydroxypropionate (PHPA) Poly-β-hydroxybutyrate (PBA)Poly-σ-valerolactone Poly-β-alkanoic acids Poly-β-malic acid (PMLA)Poly-ε-caprolactone (PCL) Pseudo-Poly(Amino Acids) Starch Trimethylenecarbonate (TMC) Tyrosine based polymers

The appropriate polymer matrix or material to be processed in practicingthe present invention may be determined by several factors including,but not limited to, the desired mechanical and material properties, thesurgical application for which the implant device is being produced, andthe desired degradation rate of the device in its final application.

The previously mentioned polymeric materials may also be compounded withone or more additive materials. The additive materials may serve variousfunctions, including, but not limited to, serving to reinforce thepolymer matrix material, and serving to deliver therapy or beneficialagents to the body. Examples of reinforcing additive materials includeceramics (e.g., hydroxyapatite, tricalcium phosphate (TCP), etc.),fibrous materials (e.g., fibers, whiskers, threads, yarns, meshes, nets,weaves, etc.), or particulates (e.g., microspheres, microparticles,beads, etc.) In those embodiments where at least one fibrousreinforcement is incorporated, the reinforcing fiber may be in anysuitable form (e.g., chopped, short, long, continuous, individual,bundled, weaved, etc.) The reinforcing additive material may becomprised of similar or different material than the polymer matrixmaterial. Suitable reinforcement material may include the previouslymentioned and most widely used bioabsorbable polymers, the resorbablepolymers of Table 1 above, their copolymers and their stereocopolymers,as well as reinforcement materials such as ceramics, metals andbioactive glasses and their compounds. Reinforcement material may benon-bioabsorbable material, and may also be used in conjunction with abioabsorbable polymer matrix material and be processed through themethod of the present invention to form a bone-treating device. Othernon-limiting examples of suitable materials that may be added to thepolymer material are listed in Table 2. TABLE 2 Reinforcing Materialssuitable for use in the Present Invention Alginate Calcium CalciumPhosphate Ceramics Chitosan Cyanoacrylate Collagen Dacron Demineralizedbone Elastin Fibrin Gelatin Glass Gold Hyaluronic acid Hydrogels Hydroxyapatite Hydroxyethyl methacrylate Hyaluronic Acid Nitinol Oxidizedregenerated cellulose Phosphate glasses Polyethylene glycol PolyesterPolysaccharides Polyvinyl alcohol Radiopacifiers Salts Silicone SilkSteel (e.g. Stainless Steel) Synthetic polymers Titanium

The additive materials may also comprise biologically active agents(e.g., therapeutics, beneficial agents, drugs, etc.) that are deliveredto the living being upon implantation of the device. The additivematerial may comprise a substance that serves to encourage tissueingrowth into the device (e.g., TCP, hydroxyapatite, etc.) The additivematerials may also serve as a drug delivery mechanism, wherein abiologically active agent is coated onto or mixed with the polymericmaterial. Alternatively, the biologically active agent may be coatedonto or contained within other additive material that is then added tothe polymer. The therapy delivery may occur rapidly once implanted (asin the case of a surface coating), or alternatively, longer-term drugdelivery is contemplated and may be achieved, where the drug deliveryoccurs for all or a portion of the duration of the implant'sdegradation. Examples of biologically active agents that may bedelivered in the device are shown in following Table 3. These materialsare only representative of the classes or groups of materials andcombinations of materials, which can be used in the practice of thecurrent invention, although some specific examples are given. TABLE 3Examples of Biological Active Ingredients Adenovirus with or withoutgenetic material Alcohol Amino Acids   L-Arginine Angiogenic agentsAngiotensin Converting Enzyme Inhibitors (ACE inhibitors) Angiotensin IIantagonists Anti-angiogenic agents Antiarrhythmics Anti-bacterial agentsAntibiotics   Erythromycin   Penicillin Anti-coagulants   HeparinAnti-growth factors Anti-inflammatory agents   Dexamethasone   Aspirin  Hydrocortisone Antioxidants Anti-platelet agents   Forskolin   GPIIb-IIIa inhibitors     eptifibatide Anti-proliferation agents   RhoKinase Inhibitors    (+)-trans-4-(1-aminoethyl)-1-(4-pyridylcarbamoyl)   cyclohexane Anti-rejection agents   Rapamycin Anti-restenosis agents  Adenosine A_(2A) receptor agonists Antisense Antispasm agents  Lidocaine   Nitroglycerin   Nicarpidine Anti-thrombogenic agents  Argatroban   Fondaparinux   Hirudin   GP IIb/IIIa inhibitorsAnti-viral drugs Arteriogenesis agents   acidic fibroblast growth factor(aFGF)   angiogenin   angiotropin   basic fibroblast growth factor(bFGF)   Bone morphogenic proteins (BMP)   epidermal growth factor (EGF)  fibrin   granulocyte-macrophage colony stimulating factor (GM-CSF)  hepatocyte growth factor (HGF)   HIF-1   insulin growth factor-1(IGF-1)   interleukin-8 (IL-8)   MAC-1   nicotinamide   platelet-derivedendothelial cell growth factor (PD-ECGF)   platelet-derived growthfactor (PDGF)   transforming growth factors alpha & beta (TGF-.alpha.,TGF-     beta.)   tumor necrosis factor alpha (TNF-.alpha.)   vascularendothelial growth factor (VEGF)   vascular permeability factor (VPF)Bacteria Beta blocker Blood clotting factor Bone morphogenic proteins(BMP) Calcium channel blockers Carcinogens Cells Chemotherapeutic agents  Ceramide   Taxol   Cisplatin Cholesterol reducers Chondroitin CollagenInhibitors Colony stimulating factors Coumadin Cytokines prostaglandinsDentin Etretinate Genetic material Glucosamine Glycosaminoglycans GPIIb/IIIa inhibitors   L-703,081 Granulocyte-macrophage colonystimulating factor (GM-CSF) Growth factor antagonists or inhibitorsGrowth factors   Bone morphogenic proteins (BMPs)   Core binding factorA   Endothelial Cell Growth Factor (ECGF)   Epidermal growth factor(EGF)   Fibroblast Growth Factors (FGF)   Hepatocyte growth factor (HGF)  Insulin-like Growth Factors (e.g. IGF-I)   Nerve growth factor (NGF)  Platelet Derived Growth Factor (PDGF)   Recombinant NGF (rhNGF)  Tissue necrosis factor (TNF)   Transforming growth factors alpha(TGF-alpha)   Transforming growth factors beta (TGF-beta)   VascularEndothelial Growth Factor (VEGF)   Vascular permeability factor (UPF)  Acidic fibroblast growth factor (aFGF)   Basic fibroblast growthfactor (bFGF)   Epidermal growth factor (EGF)   Hepatocyte growth factor(HGF)   Insulin growth factor-1 (IGF-1)   Platelet-derived endothelialcell growth factor (PD-ECGF)   Tumor necrosis factor alpha (TNF-.alpha.)Growth hormones Heparin sulfate proteoglycan HMC-CoA reductaseinhibitors (statins) Hormones   Erythropoietin ImmoxidalImmunosuppressant agents inflammatory mediator Insulin InterleukinsInterlukin-8 (IL-8) Interlukins Lipid lowering agents Lipo-proteinsLow-molecular weight heparin Lymphocites Lysine MAC-1 Methylationinhibitors Morphogens Nitric oxide (NO) Nucleotides Peptides PolyphenolPR39 Proteins Prostaglandins Proteoglycans   Perlecan Radioactivematerials   Iodine - 125   Iodine - 131   Iridium - 192   Palladium 103Radio-pharmaceuticals Secondary Messengers   Ceramide SomatomedinsStatins Stem Cells Steroids Thrombin Thrombin inhibitor ThrombolyticsTiclid Tyrosine kinase Inhibitors   ST638   AG-17 Vasodilators  Histamine   Forskolin   Nitroglycerin Vitamins   E   C Yeast Ziyphifructus

The inclusion of groups and subgroups in Table 3 is exemplary and forconvenience only. The grouping does not indicate a preferred use orlimitation on use of any drug therein. That is, the groupings are forreference only and not meant to be limiting in any way (e.g., it isrecognized that the Taxol formulations are used for chemotherapeuticapplications as well as for anti-restenotic coatings). Additionally, thetable is not exhaustive, as many other drugs and drug groups arecontemplated for use in the current embodiments. There are naturallyoccurring and synthesized forms of many therapies, both existing andunder development, and the table is meant to include both forms.

The additive materials may also comprise plasticizers or other materialsto provide desirable application properties to the final implant device.Plasticizers or materials that enhance the malleability of the materialmay allow the processing of the material of the present invention tooccur at lower temperatures, providing various benefits (e.g., reducedpolymer and additive material breakdown, reduced cooling times, reducedcosts, increased productivity, increased polymer chain alignment, etc.).

The following description with reference to the associated figuresdescribes the features of the present invention, wherein like numbersrefer to like components.

The present invention consists of a method for producing a surgicalimplant, such as a tissue fixation device, or a bone-treating device,which begins with a provided mass of polymer material called a slug orbillet of determinate length. With reference to FIGS. 1, 2A and 2B, theslug of material 4 may be provided having an initial shape or geometry.Preferably, the slug 4 is provided in a simple cylindrical form as shownin FIG. 1, although the slug may be provided in other general shapes,for example, as shown by the alternative slug configurations depicted inFIGS. 2A and 2B.

As can be seen in FIGS. 3A and 3B, the slug 4 may also be providedhaving a section of more complex geometry, internally and/or externallyof the predominate general slug shape. This complex geometry included inthe slug may take on the form of geometry that is indicative of thefinal bone treating device or implant, as can be seen in FIGS. 3A and B. FIG. 3B depicts an example of complex external geometry on apredominately simple cylindrical slug, while FIG. 3A depicts an exampleof complex internal geometry on a similar cylindrical slug. The complexgeometry may be any additional formation than would occur with a generalshaped slug in a simple shape (e.g., cylinder, box, conical, etc.)

The complex geometry may be incorporated into the slug through typicalmelt processing techniques such as injection molding or throughtraditional machining techniques or alternatively through the method ofthis present invention. The complex geometries shown in FIGS. 3A and 3Bmay be final device geometry that is maintained throughout theprocessing method of the device and such complex geometry in thisexample could be used as the interface between the final device and thesurgical instrument, a driver of a fastener for example. Complexgeometry is not limited to the designs shown in FIGS. 3A and 3B, butparticular to the geometry of the final implant or device and the extentof feasibility with the processing method described in the presentinvention.

The slug or billet 4 is described as having a determinate length in thatthe length and subsequent mass of the slug has been determined and basedon the final implant, tissue fixation device or bone treating device toresult from the method and tooling utilized and described in the presentinvention.

The raw material for the provided slug material can be processed andformed through standard manufacturing techniques known in the art,including, but not limited to, traditional melt processes forthermoplastics (e.g., injection molding, single screw extrusion, twinscrew extrusion, compression molding, etc., and combinations thereof),as well as through the method of this present invention. Techniquesutilized for manufacturing a slug may impart orientation to the polymerstructure, as has been discussed earlier, with reference to U.S. Pat.No. 4,968,317. The creation or increase of orientation in the polymerstructure results in a stronger material, relative to a similar polymermaterial lacking equivalent orientation. The preferred material for theprovided slug will have at least some orientation, such as a polymerslug material that has been processed through an extrusion process,which inherently creates a degree of molecular orientation. An alternateembodiment may provide a semi or randomly oriented polymer slugmaterial, such as that resulting from injection molding, which offerslimited preferred orientation and is heavily dependant upon toolingdesign and process conditions. However, melt processes not resulting inhighly oriented material, such as injection molding, offer advantagesthat may be necessary in terms of incorporating complex geometry in theslug as shown in FIGS. 3A and 3B. The provided slug material may also bemachined to desired geometry and/or tolerances through typical machiningtechniques following initial typical melt processing. Independent of thedegree of molecular orientation of the beginning slug or the method usedfor fabricating the beginning slug, the final material or device formedby the method of the present invention will result in improvedorientation in comparison to the originally provided slug or billet.

The material of the provided slug is processed through the practice ofthe present invention to arrive at the final desired implant, tissuefixation device or bone treating device, therefore, any additivematerials added to the provided polymer slug are incorporated into thefinal product of the invention. For example, a fiber reinforced slugresults in a fiber reinforced implantable device, similarly, a slugincorporating drug therapy measures will result in an implantincorporating drug therapy measures.

With reference to FIG. 4A, the preferred arrangement of the tooling usedfor the method of the present invention includes a press ram 1, a barrel2 or similar holding and/or heating chamber as defined by barrel tooling22, and a die cavity 3 defined by die cavity tooling 33. The slug 4 isplaced in the barrel portion 2 of the barrel tooling 22. The barreltooling 22 may be a separate component that has been affixed to the diecavity tooling 33 or alternatively may be an integral one-piece designcomprising both the barrel tooling 22 and the die cavity tooling 33.

In an alternate, and fundamentally reversed arrangement depicted by FIG.4B, the die cavity tooling 33, defining the die cavity 3 isoperationally attached to the press ram 1. The actuation of the pressram 1 drives the die cavity tooling against the polymer slug 4,contained within the barrel 2, as defined by the barrel tooling 22.

The barrel tooling 22 and die cavity tooling 33 shown in FIGS. 4A and 4Bare individually depicted as single piece tooling, respectively formingthe barrel geometry 2 and the die cavity geometry 3. It is recognizedthe particular construction of the barrel tooling 22 and die cavitytooling 33 may beneficially comprise multiple and separable components,particularly a two piece or multiple piece design in which it ispreferable, but not necessary, for any parting line of tooling to runparallel with the longitudinal axis of the formed bone treating deviceor implant. FIG. 8 depicts a cross-sectional view of an exemplaryseparable, two-piece die cavity tooling 33 consisting of separable diecavity 3 with the parting line 11 of the tooling running parallel withthe longitudinal axis of the formed device with device shank 5 anddevice head 6.

Referring again to the preferred embodiment depicted by FIG. 4A, butapplicable to other described embodiments as well, the barrel 2 formedby the barrel tooling 22 should preferably mimic the outside geometry ofthe slug 4 to be placed within the barrel, though not necessary.Furthermore, the barrel tooling 22 and die cavity tooling 33 arepreferably temperature controlled, incorporating a mechanism to provideheating and/or cooling (not shown). This is to allow proper heattransfer from the barrel tooling 22 to the slug 4. In operation, theslug 4 within the barrel 3 may be heated to a temperature between theglass transition temperature and melting temperature (as in asemi-crystalline polymer) of the material comprising the slug 4 or asapplicable based on the material of the slug. The barrel 2 and barreltooling 22 are heated to this desired temperature either prior to theslug 4 being placed in the barrel 2 or after the slug is placed in thebarrel. Alternatively, the processing method for producing the finaldevice also allows for the slug 4 to be heated to a temperature, againbetween the glass transition temperature and the melting pointtemperature of the slug material, prior to being placed in the barrel 2.In this case, the barrel may also be pre-heated.

In an embodiment, a temperature gradient extending from the barrel 2 andthe slug 4 to the die cavity 3 may be induced. The maximum and minimumtemperature within this temperature gradient is preferably maintainedbetween the glass transition temperature of the slug material and themelting temperature of the slug material. It is recognized there may bebenefit in temperature set points that are (at least temporarily)somewhat higher or lower than the recorded glass transition and meltingtemperatures of the polymer, in order to account for heat transferproperties, or to intentionally derive a localized temperaturevariation. This temperature gradient may consist of a higher temperatureat the barrel 2 and slug 4 location than at the die cavity 3 or with thegradient reversed, in which the highest temperature of the temperaturegradient exists at the die cavity 3. In this embodiment, the surgicaldevice or implant may have been processed by the method of the presentinvention at different temperatures along the length of the device. Thetemperature gradient when processing the material may influence thedegree of orientation in the polymer, thereby increasing the mechanicalproperties along the longitudinal direction of the final surgicalimplant, tissue fixation device or bone treating device. Followingheating of the slug 4 to the desired temperature and/or for the desiredduration, the slug is driven by the actuation of press ram 1 into thedie cavity 3 portion of the die cavity tooling 33. In a preferredembodiment, the geometry of the end of the press ram 1 in contact withthe slug 4 is formed as a flat surface; however, the end mayalternatively possess internal and external complex geometry. Complexgeometry for the press ram 1 may include external complex geometry asshown in FIG. 5A, or internal complex geometry as shown in FIG. 5B.Either external or internal complex geometry may mimic geometry of thefinal device and cause the final device to be formed into the slug 4during pressing. For example, the geometry shown in FIGS. 5A and 5B mayform final bone treating device geometry that is used at the interfaceof the device and a surgical instrument (e.g. a driver of a fastener).Alternatively, the complex geometry shown in FIGS. 5A and 5B mayinversely correspond to the complex geometry that is already present inthe provided slug as previously discussed with reference to FIGS. 3A and3B.

The ram 1 may or may not be pre-heated prior to pressing the slug 4. Theram may be driven by typical mechanical means known in the art (e.g.,hydraulic, electric, rack & pinion etc.) However, the control and/orvariability of speed, positioning, force and dwell may be varied todetermine the mechanical and polymer alignment properties of the finalpart (i.e., the implantable device), and are essential in forming afinal implant, tissue fixation device or bone treating device per themethod of the present invention. In one embodiment, the actuation of theram 1 forces the slug 4 into a dry cavity 3, or alternatively, thepressing of the slug may employ lubrication in order to facilitate theflow of the polymer slug 4 into the cavity 3.

In an alternate embodiment, the implant device may be formed by asimilar process as described above, however relying on hydrostaticextrusion (not shown), wherein the actuation of the ram exerts pressureupon a fluid surrounding the slug in the barrel, forcing the slug intothe die cavity. As is known in the art, one of the benefits ofhydrostatic extrusion is the lubrication afforded by thenon-compressible medium surrounding the slug. The device manufactured inthe practice of the present invention features varied zones of polymeralignment. This zone variation occurs due to differences in how someareas of the slug 4 undergo deformation in conforming to the die cavity3 as the ram exerts pressure, resulting in greater elongation andaccordingly greater alignment in some areas, while other regions of theslug experience less deformation and therefore feature less alignment.

With reference again to FIG. 4A, the die cavity portion 3 of the diecavity tooling 33 consists of geometry in part or in full of the finalbone treating device or implant to be formed. For example, where theimplant to be manufactured is a tissue or bone fastener, the die cavitytooling 33 may consist of the shank diameter 5 of the bone fastener andalso the head geometry 6 of the bone fastener device . The die cavity 3consists of reduction in cross sections from one final part geometry tothe next. For example, the die cavity depicted in FIG. 4A varies incross section from the bone fastener head diameter 6 to the shankdiameter 5 of the bone fastener form. The reduction in cross sectionaffects the mechanical deformation and further orients the polymermolecules and molecular segments, thereby resulting in increasedmechanical properties such as shear and bend resistance in the desiredlocation. This occurs as the polymer slug material 4 that is driven intothe shank diameter portion 5 of the die cavity 3 undergoes significantlymore deformation and elongation in extending into the shank area,thereby creating significant alignment of the polymer molecules, whencompared to the slug 4 material that is formed into the head portion 6of the die cavity 3, where less deformation and elongation is required,resulting in significantly less reorientation of the polymer molecules.The desired location for increased-mechanical properties such as shearand bend resistance, in this example, is the shank diameter 5 of a bonefastener.

In practice of the present invention, the polymer slug 4 is pressed intothe die cavity 3 by the actuation of ram press 1, causing the slug toconform to, and completely fill, the die cavity, or alternatively to atleast partially fill the die cavity. The cavity may be a substantiallyenclosed area defined by the die cavity tooling 33 having only oneopening for the introduction and removal of the polymer material (asdepicted by the die cavity 3 of FIG. 4A). In another embodiment, the dietooling may feature a second opening away from the ram press 1 to allowfor the introduction of an ejection device or pin penetrating throughthe die cavity tooling, as can be seen in FIGS. 6 and 7.

The ejection device of FIG. 6 features a pin 7 that extends through thedie cavity tooling, and extends into the die cavity 3. In thisembodiment, the ejection pin further serves to add to the geometry ofthe final device (e.g., by adding complex geometry as described above).In the example depicted in FIG. 6, the pin 7 may serve to create a slotor a hollow core in the device, created as the pressed polymer slugmaterial surrounds the protruding pin or coring.

In another embodiment, the ejection device depicted in FIG. 7 may serveas a temporary present die cavity closure, until ejection of the bonetreating device is required. Ejection or removal of the bone treatingdevice is preferably performed following proper cooling in the diecavity. The ejection device 7 may optionally consist of geometry 10particular to the final bone treating device or implant. In theembodiment depicted by FIG. 7, the ejection pin 7 consists of geometryspecific to the tip of a bone treating fastener.

The reduction or variation in cross-section and the inducing of zones ofvariable alignment through the pressing method described in the presentinvention does not need to only take place in the die cavity tooling 33and die cavity 3, as has been previously described. In an alternativeembodiment depicted by FIG. 9, the mechanical strengths of the shapedpolymer material may further be increased by continuing to addstep-downs in cross-section or increasing the number of variations incross-section that further align the polymer molecular structure. Thismay be defined or described as double or multiple-pressing and may takeplace within either the barrel 2 of the barrel tooling 22, the cavity 3of the cavity tooling 33, or both. FIG. 9 depicts an example of multiplereductions in cross section further aligning the polymeric molecularstructure and obtaining a near net or final shape bone treating deviceor implant with varying zones or degrees of alignment. In FIG. 9, forexample, but not limited to this location, the multiple reductions incross section take place in both the barrel 2 of the barrel tooling 22and also the die cavity 3 of the die cavity tooling 33. The locations ofthe reductions in cross-section and subsequent varying zones ofalignment are shown by 12 and 13.

Alternatively, a way to increase the number of reductions in crosssection and continue to increase the subsequent mechanical properties isto obtain an implant device through the method of the present inventionand to repeat the method of the present invention one or more additionaltimes. This is also an opportunity to not only continue to reduce thecross-section through the pressing operation and increase mechanicalproperties, but also to continue to add different geometry through theuse of different tooling components (e.g., press ram 1, die cavity 3,etc.), the application of which may continue to accomplish a near netshape of the final bone treating device or implant and further reduceand/or eliminate subsequent machining or related processes.

After pressing per the method of the present invention, the device orimplant may be cooled in the die components, either under pressure fromthe ram or another source, or alternatively the implant may be cooledafter release of the pressure. Cooling may be controlled by providingfor at least one cooling rate, and may vary locally within the diecomponents, and/or temporally. The various cooling rates may be employedas required with respect to the material and design to be cooled.

The implant material, while still in the die cavity 3, may further bere-heated between the glass transition temperature (or thereabouts), andthe melt temperature (or thereabouts), of the material and then thecooling process, either with or without pressure, and one or multiplecooling rates, may be employed, as described above. This heating and/orcooling cycling may be employed as required with respect to thematerial, the design, and the advantages and/or disadvantages that suchheating and/or cooling cycling may have on the final desired properties.For example, an amorphous material may require a different coolingrate(s) and/or a different temperature set point during a re-heatingcycle than might a partially crystalline material to gain desiredstrength increases due to molecular aligning the respective polymerstructure.

In a preferred embodiment, all stages in the manufacturing of thepolymer implant device, from slug placement, ram pressing, slug formingwithin the die cavity, and ejection, are along a common longitudinalaxis, which in the case of the simple cylindrical geometry shown in FIG.1 is the axis of molecular orientation.

The above described operational processes and practices may be performedto form an implantable device with zones of variable alignment of thepolymer structure, zones of varying cross-section and preferably, finalpart geometry of the implantable device.

Thus, since the invention disclosed herein may be embodied in otherspecific forms without departing from the spirit or generalcharacteristics thereof, some of which forms have been indicated, theembodiments described herein are to be considered in all respectsillustrative and not restrictive, by applying current or futureknowledge. The scope of the invention is to be indicated by the appendedclaims, rather than by the foregoing description, and all changes whichcome within the meaning and range of equivalency of the claims areintended to be embraced therein.

1) A device suitable for implantation in a living being, said devicecomprising an at least partially crystalline polymer material, saidpolymer material comprising a plurality of zones having polymermolecular orientation and cross section, wherein at least one zone ismore highly oriented than at least one other zone. 2) The device ofclaim 1, wherein said polymer material comprises a resorbable polymer.3) The device of claim 2, wherein said resorbable polymer is selectedfrom the group consisting of PLA, PGA, PGA/PLLA, DLPLA, and combinationsthereof. 4) The device of claim 1 further comprising additive materialsselected from the group consisting of ceramics, fibrous materials,particulate materials, biologically active agents, plasticizers andcombinations thereof. 5) A method for the manufacture of a devicesuitable for implantation in a living being, said method comprising thesteps of: a) providing a polymer slug, barrel, die cavity tooling, andram press, wherein said die cavity tooling defines a die shape; b)placing said polymer slug between said ram press and die cavity tooling;c) actuating said ram press in order to apply pressure upon said polymerslug, thereby forcing said polymer slug to conform to said die shape,wherein said polymer slug is formed into a device comprising zones ofvariable alignment of the polymer structure, and zones of varyingcross-section; and d) removing said device from said die cavity tooling.6) The method of claim 5, further comprising the step of: e) machiningsaid device to a finished product. 7) The method of claim 5, whereinprior to ram press actuation, said polymer slug is heated to atemperature having a lower range about a glass transition temperatureand an upper range about a melting temperature of the polymer, beforesaid polymer slug is forced to conform to said die shape. 8) The methodof claim 7, wherein said heating creates a temperature gradient in saidpolymer slug, die cavity tooling and barrel. 9) The method of claim 7,wherein prior to removing said device from said die cavity tooling, saiddevice is reheated and allowed to cool. 10) The method of claim 5,wherein said polymer slug comprises a resorbable polymer. 11) The methodof claim 10, wherein said resorbable polymer is selected from the groupconsisting of PLA, PGA, PGA/PLLA, DLPLA, and combinations thereof. 12)The method of claim 5, wherein said polymer slug provided furthercomprises additive materials. 13) The method of claim 12, wherein saidadditive materials are selected from the group consisting of ceramics,fibrous materials, particulate materials, biologically active agents,plasticizers and combinations thereof. 14) The method of claim 5,wherein said die cavity tooling comprises a head portion and a shankportion, wherein said head portion has a larger cross section than saidshank portion. 15) The method of claim 5, wherein said die cavitytooling is temperature controlled. 16) The method of claim 5, whereinsaid barrel is temperature controlled. 17) The method of claim 5,wherein said ram press further comprises complex geometry. 18) Themethod of claim 5, wherein said die cavity tooling is not unitary butrather comprises a plurality of pieces capable of fitting together. 19)The method of claim 5, wherein said polymer slug further comprisescomplex geometry. 20) The method of claim 5, wherein said die cavitytooling further comprises an ejection pin. 21) The method of claim 20,wherein said ejection pin serves to form an end of said polymer slug.22) A method for the manufacture of a device suitable for implantationin a living being, said method comprising the steps of: a) providing apolymer slug, die cavity tooling, and ram press, wherein said die cavitytooling defines a die shape; b) placing said polymer slug between saidram press and die cavity tooling; c) actuating said ram press in orderto apply pressure upon said polymer slug, thereby forcing said polymerslug to conform to said die shape, wherein said polymer slug is formedinto a device comprising zones of variable alignment of the polymerstructure, and zones of varying cross-section; d) removing said devicefrom said die cavity tooling; e) placing said device between said rampress and a second die cavity tooling, wherein said second die cavitytooling defines a second die shape; f) actuating said ram press in orderto apply pressure upon said device, thereby forcing said device toconform to said second die shape, wherein said device is formed into atwice pressed device comprising zones of increased alignment of thepolymer structure, and zones of varying cross-section. 23) A devicesuitable for implantation in a living being, said device comprisingzones of variable alignment of the polymer structure, and zones ofvarying cross-section, and wherein said device is made by the processof: a) providing a polymer slug, barrel, die cavity tooling, and rampress, wherein said die cavity tooling defines a die shape; b) placingsaid polymer slug between said ram press and die cavity tooling; c)actuating said ram press in order to apply pressure upon said polymerslug, thereby forcing said polymer slug to conform to said die shape,wherein said polymer slug is formed into said device comprising saidzones of variable alignment of the polymer structure, and said zones ofvarying cross-section; and d) removing said device from said die cavitytooling. 24) The device made by the process of claim 23, the processfurther comprising the step of: e) machining said device to a finishedproduct. 25) The device made by the process of claim 23, wherein priorto ram press actuation, said polymer slug is heated to a temperaturehaving a lower range about a glass transition temperature and an upperrange about a melting temperature of said polymer slug before saidpolymer slug is forced to conform to said die shape. 26) The device ofclaim 25, wherein said heating creates a temperature gradient in saidpolymer slug, die cavity tooling and barrel. 27) The device of claim 25,wherein prior to removing said device from said die cavity tooling, saiddevice is reheated and allowed to cool. 28) The device made by theprocess of claim 23, wherein said polymer slug comprises a resorbablepolymer. 29) The device of claim 28, wherein said resorbable polymer isselected from the group consisting of PLA, PGA, PGA/PLLA, DLPLA, andcombinations thereof. 30) The device made by the process of claim 23,wherein said polymer slug provided further comprises additive materials.31) The device of claim 30, wherein said additive materials are selectedfrom the group consisting of ceramics, fibrous materials, particulatematerials, biologically active agents, plasticizers and combinationsthereof. 32) The device made by the process of claim 23, wherein saiddie cavity tooling comprises a head portion and a shank portion, whereinsaid head portion has a larger cross section than said shank portion.33) The device made by the process of claim 23, wherein said die cavitytooling is temperature controlled. 34) The device made by the process ofclaim 23, wherein said barrel is temperature controlled. 35) The devicemade by the process of claim 23, wherein said ram press furthercomprises complex geometry. 36) The device made by the process of claim23, wherein said die cavity tooling is not a single piece but rathercomprises a plurality of pieces capable of fitting together. 37) Thedevice made by the process of claim 23, wherein said polymer slugfurther comprises complex geometry. 38) The device made by the processof claim 23, wherein said die cavity tooling further comprises anejection pin. 39) The device of claim 38, wherein said ejection pinserves to form an end of said polymer slug.